N-Acetyl Cysteine (NAC)
N-acetyl cysteine (NAC) is a stable form of the amino acid L-cysteine. In plain terms: NAC's recognised, authoritative uses in the UK are medicinal. It is the hospital antidote — given intravenously — for paracetamol overdose, and the mucolytic class it belongs to is one NICE says may be considered within NHS care for a long-standing chesty cough in COPD. NAC is also sold as an oral food supplement, including by Camden Medicals — but that is a separate regulatory question the UK Food Standards Agency has not settled, and there are no GB-authorised health claims for NAC. This entry leads with what UK and EU bodies actually say (see the guidance section), then presents the underlying research beneath it.
Camden Medicals editorial · Last reviewed 11 June 2026 · Next review October 2026
- Cross-checked against
- NHS
- NICE
- BNF
- EFSA
- FSA
Camden's editorial team independently graded each health claim below on the strength of the published evidence — see the grade beside every condition.
- Class
- Amino acid
- Typical daily dose
- UK food-supplement products are most commonly sold at 600 mg per capsule, with directions for one to two capsules daily (600-1,200 mg/day). Pharmacist-supplied oral mucolytic preparations on the Continent (e.g. Fluimucil) are dosed at 600 mg two to three times daily. Mental-health RCTs (Berk 2008 bipolar depression) used 1,000 mg twice daily; some psychiatric trials have gone up to 2,400-3,600 mg/day in divided doses. There is no UK-authorised dose for food-supplement use, because there is no UK-authorised health claim.
- Top use evidence
- Strong
On this page
What it is
N-acetyl cysteine, usually shortened to NAC, is the N-acetylated form of the amino acid L-cysteine. Adding the acetyl group makes the molecule more chemically stable and somewhat better absorbed by mouth than free L-cysteine, which is unstable in solution. Once inside cells, NAC is de-acetylated back to cysteine, which the body uses to build proteins and glutathione — the main intracellular antioxidant.
NAC has three quite different identities in UK pharmacy. As an intravenous infusion (Parvolex and generic NAC), it is the standard hospital antidote for paracetamol overdose and is virtually 100% effective at preventing liver damage when given within eight hours of ingestion. As a pharmacist-supplied oral medicine in some other European markets (e.g. Fluimucil), it has a long-standing role as a mucolytic in chronic respiratory disease. As a food supplement (capsules, typically 600 mg), it is sold by UK retailers including Camden Medicals — but with no UK-authorised health claims attached and with a regulatory backdrop that has been actively contested in the United States and is not explicitly settled by the UK Food Standards Agency.
At a glance
- NAC is a stable, acetylated form of cysteine — not the same thing as glutathione, though the body uses cysteine to make glutathione.
- The strongest evidence for NAC sits in two specific clinical settings: as the IV antidote for paracetamol overdose (a hospital-administered medicine, not a supplement) and as an oral mucolytic in chronic bronchitis / COPD (an effect now treated as modest by the most recent Cochrane review).
- Trial signals in mental-health adjunctive use (bipolar depression, OCD, schizophrenia, trichotillomania) are early and inconsistent. NAC is not a treatment for any UK-recognised psychiatric condition.
- There are no UK-authorised health claims for NAC. The food-supplement legal status is a quiet grey area in GB and unsettled in the US — buy from a UK retailer that names the form, declares GMP manufacture, and does not market disease-treatment claims.
- If you take nitrates (GTN, isosorbide), an anticoagulant, or have asthma, talk to your pharmacist before starting NAC.
What people use it for
Patients in hospital after a paracetamol (acetaminophen) overdose
Intravenous N-acetylcysteine is the standard UK antidote and is virtually 100% effective at preventing liver damage when started within 8 hours of ingestion. This is a hospital-administered prescription medicine — not a food supplement, and not something to attempt with capsules at home. [10,2]
Some evidenceStrongAdults with chronic bronchitis or chronic obstructive pulmonary disease (COPD)
Oral NAC and other mucolytics modestly reduce the likelihood of an acute exacerbation in adults with chronic bronchitis / COPD, with about 8 people needing 9 months of treatment to keep one extra person exacerbation-free (Poole 2019 Cochrane CD001287.pub6, moderate-certainty evidence). Effect sizes in more recent trials are smaller than in older trials. UK NHS care for COPD is the right place to discuss this — NAC mucolytic preparations on the Continent (e.g. Fluimucil) are pharmacist-supplied medicines, not food supplements. [7,11]
Some evidenceModeratePeople exploring NAC for mental-health symptoms (bipolar depression, OCD, addictions, trichotillomania)
Small RCTs (notably Berk 2008 in bipolar depression, n=75, 1 g twice daily) have shown signals on depression rating scales when NAC is added to standard psychiatric care. The signal is not consistent across larger and more recent trials, NAC is not a treatment for any UK-recognised psychiatric condition, and stopping or starting NAC alongside prescribed mental-health medication should be a conversation with your prescriber. UK NHS pathways for these conditions apply (NICE guidelines). [12,13]
Some evidenceLimitedPeople with PCOS exploring adjunctive support around ovulation
Some short trials have looked at NAC alongside standard fertility medication in polycystic ovary syndrome. Results are mixed, several individual studies have been retracted from the literature for data-integrity reasons, and no high-quality systematic review currently endorses NAC as a routine adjunct. PCOS care is a clinical pathway — NICE CKS and your GP / fertility clinic are the right sources. [14]
Popular, not provenInsufficientPeople taking NAC as a general antioxidant / liver / hangover supplement
There are no UK-authorised health claims for NAC and no robust evidence for these popular online uses. The body makes glutathione from cysteine on demand from a normal protein-containing diet; supplementing NAC in a person who is not glutathione-depleted has not been shown to add benefit at the population level. The popular framing of NAC as a hangover remedy or general cleansing aid is not supported by the evidence.
Popular, not provenInsufficient
How it works
Inside cells NAC is de-acetylated to L-cysteine, which feeds the rate-limiting step of glutathione synthesis. NAC also reduces disulfide bonds — the chemistry behind its mucolytic effect on thick respiratory mucus and behind its antidotal restoration of hepatic glutathione in paracetamol overdose.
Common myths
Myth"NAC is just a regular supplement like vitamin C"
RealityIt is not. NAC's primary clinical identity is as a hospital antidote (IV, paracetamol overdose) and a pharmacist-supplied mucolytic medicine in some markets. Its food-supplement status in the UK is a quiet grey area: the FSA Novel Foods register does not list it, the US FDA enforcement position was actively contested in 2020-2022, and there are no UK-authorised health claims attached to it. That makes it unlike the vitamins and minerals on the GB NHC Register, which have authorised function claims and clear consumer contexts. [4]
Myth"NAC cures depression"
RealityIt does not. NAC is not licensed in the UK for any psychiatric condition. The most-cited supportive trial (Berk 2008, n=75 bipolar depression maintenance) showed an improvement on a depression rating scale at 24 weeks but no effect on time to mood episodes, with benefit lost at washout; signal in larger and more recent trials has been inconsistent. Marketing copy that promises antidepressant effects from a food-supplement capsule goes beyond the evidence and beyond what UK supplement-marketing rules permit. [12]
Myth"NAC equals glutathione"
RealityNot quite. NAC supplies cysteine, the rate-limiting amino acid in glutathione synthesis. The body builds glutathione from cysteine, glutamine, and glycine. Oral glutathione itself is largely broken down in the gut. NAC raises intracellular glutathione meaningfully in the scenario where it is most needed (paracetamol overdose, where the toxic metabolite NAPQI has depleted hepatic glutathione); in healthy adults eating an ordinary protein-containing diet, glutathione is not generally rate-limited. [10]
Myth"It is safe to combine NAC with paracetamol because NAC is the antidote"
RealityThat logic does not transfer. The IV antidote use is for an overdose situation under hospital supervision, with weight-based dosing and a precise infusion regimen. Oral NAC in capsules taken alongside ordinary paracetamol does not make paracetamol safer or expand its safe dose window. If you have taken more paracetamol than the box allows, contact NHS 111 or A&E — paracetamol overdose damage is delayed and silent. [3]
Myth"NAC prevents long COVID"
RealityNo high-quality RCT supports NAC for prevention or treatment of long COVID. Claims to that effect proliferated online in 2020-2022. UK NHS post-COVID services do not list NAC. Long-COVID symptoms often have other treatable causes; see a GP rather than self-treating. [15]
Common online questions
Synthesised from the questions UK shoppers most often ask online about N-Acetyl Cysteine (NAC). Each answer is editorial and links to its evidence in the Sources list below.
Is NAC the same as glutathione?
No. NAC is a small, stable molecule that the body de-acetylates to L-cysteine, which is then one of three building blocks of glutathione (alongside glutamine and glycine). Oral glutathione itself is largely broken down in the gut, so the popular framing of NAC as a "glutathione precursor" is technically correct but operationally over-sold: in healthy adults the body already makes plenty of glutathione from a normal protein-containing diet. NAC raises hepatic glutathione meaningfully in the specific scenario where it is most established — paracetamol overdose, where glutathione has been depleted by the toxic metabolite NAPQI. [10]
Can I take NAC with paracetamol to be safe?
No. The hospital antidote use is for an actual overdose situation, with IV dosing, monitoring, and a precise nomogram. Taking oral NAC alongside ordinary paracetamol does not make paracetamol safer; it does not give you a margin to take higher paracetamol doses; and it can interact with other medicines you take. Stick to the paracetamol on the box. If you have taken more paracetamol than the maximum daily dose, contact NHS 111 or A&E immediately, even if you feel fine — liver damage from overdose can be silent for days. [3]
Will NAC cure my hangover?
There is no good evidence that NAC has any effect on hangovers. The biological story marketers tell — that alcohol depletes glutathione and NAC tops it up — is plausible in cell-culture and animal models, but high-quality human RCTs in hangover prevention are absent. The UK NHS guidance on hangovers is unglamorous: time, water, paracetamol or ibuprofen for headache (within their normal limits), and food. Drinking less is the only intervention with a reliable evidence base. [16]
Does NAC treat depression?
No. NAC is not licensed in the UK for depression and is not a treatment for it. There are early-signal RCTs — most prominently Berk 2008 in bipolar depression — that are often cited online to imply a treatment effect; the trials were small, the signal has been inconsistent in larger and more recent studies, and effects washed out when treatment stopped. If you are experiencing depression, the NHS pathway (GP, talking therapy, prescribed antidepressants where indicated) is the right route. Do not stop or substitute prescribed mental-health medication on the basis of online NAC marketing. [12,13]
Is NAC banned or unsafe to sell as a supplement?
The picture is unsettled. The US FDA from 2020-2022 took the position that NAC's prior approval as a drug excluded it from being marketed as a dietary supplement, then softened in 2022 with a guidance document allowing enforcement discretion. In the UK, the Food Standards Agency does not list N-acetylcysteine on the GB Novel Foods register as authorised, under-assessment, or unauthorised. UK retailers (Camden Medicals included) do sell NAC capsules; the regulatory backdrop is quiet, not endorsed. There are no UK-authorised health claims for NAC, so it must be sold and described without disease-treatment language. [4]
Should I take NAC long-term?
There is no UK consensus on long-term NAC supplementation in otherwise healthy adults, because there are no UK-authorised use cases that would establish a duration. The published mucolytic trials run from a few weeks to about three years; the bipolar-depression RCT was 24 weeks. If you are taking NAC for a specific reason your pharmacist or GP supports, follow their guidance. Otherwise the question to ask is what evidence-supported outcome you are expecting, and whether you have the bloodwork (e.g. liver enzymes) that would tell you it is working. [7,12]
What about NAC for long COVID?
Online claims that NAC treats long COVID multiplied during 2020-2022, but the evidence is anecdotal. There are no large, high-quality RCTs supporting NAC as a long-COVID treatment, and NHS post-COVID syndrome services do not recommend it. The UK National Institute for Health and Care Research and the Cochrane post-COVID review register are the right places to follow as evidence accumulates. Long-COVID symptoms can have other treatable causes — see a GP rather than self-treating with supplements. [15]
🔬 Camden’s evidence review
The research Camden reviewed, graded on its strength. This is our own appraisal — it sits beneath the official guidance above, never above it.
Paracetamol (acetaminophen) overdose — hospital antidote
StrongEvidencestrongUK guidance leads here and is unambiguous. The MHRA describes intravenous acetylcysteine as the established hospital antidote for paracetamol overdose, with an authorised infusion regimen and steps to reduce reaction risk; the NHS tells anyone who may have taken too much paracetamol to seek urgent care (NHS 111 or A&E) even when they feel well, because liver harm can take days to show. Beneath that guidance, the primary literature Camden reviewed is consistent: Prescott's 50-year retrospective in the British Journal of Clinical Pharmacology (2023) traces the antidote's evidence base, the move to simpler infusion regimens, and the lower rate of anaphylactoid reactions with slower initial infusion rates. This is a prescription medicine given in hospital — it is not a use case for food-supplement capsules, and home self-treatment of an overdose is not a substitute for emergency care. [10,2]
Chronic bronchitis and COPD — mucolytic effect
ModerateEvidencemoderateUK guidance leads. NICE (NG115) says a mucolytic medicine — the class that includes acetylcysteine and carbocisteine — may be considered for a person with COPD who has a chronic cough that brings up phlegm, should be continued only if symptoms such as cough frequency improve, and should not be used routinely to prevent exacerbations in stable COPD. Beneath that position, the research Camden reviewed: Poole 2019 (Cochrane CD001287.pub6, 38 trials, 10,377 participants) found oral mucolytics — N-acetylcysteine, carbocysteine, erdosteine, ambroxol — modestly reduce the likelihood of an exacerbation (Peto OR 1.73 for being exacerbation-free, NNT≈8 over 9 months, moderate-certainty evidence), with smaller effects in more recent trials and limited effect on lung function and quality of life. Stey 2000 (Eur Respir J, 11 trials, 2,011 patients) reported a larger effect (NNT≈6); the more recent Cochrane signal is the conservative reading. Mucolytic use in COPD is an NHS clinical decision, not a food-supplement use. [7,11]
Bipolar depression and other psychiatric indications — adjunctive use
LimitedEvidencelimitedUK guidance leads, and it is cautionary: no NICE guideline recommends NAC for bipolar disorder, depression, OCD, schizophrenia or any other psychiatric condition, and NAC is not licensed in the UK for any of them — NHS mental-health pathways apply. Beneath that, the research Camden reviewed: Berk 2008 (Biological Psychiatry, n=75) randomised adults with bipolar disorder in the maintenance phase to NAC 1 g twice daily or placebo for 24 weeks added to usual care; the NAC arm improved on the Montgomery–Åsberg Depression Rating Scale (MADRS mean difference -8.05) but showed no effect on time to a mood episode, with benefit lost after washout. Larger and more recent trials across mood disorders, schizophrenia, OCD and addictions have been inconsistent, and the Raghu/Berk 2021 review (Curr Neuropharmacol) describes the field as biologically plausible but not yet established. [12,13]
Autism spectrum disorder — adjunctive use in children
LimitedEvidencelimitedUK guidance leads: NAC is not a UK-licensed treatment for autism spectrum disorder and no NICE guideline recommends it; NHS autism pathways apply. Beneath that, the research Camden reviewed: Lee 2020 (Aust N Z J Psychiatry) meta-analysed five small RCTs of NAC in children with ASD (8–12 weeks) and reported pooled improvements on the Aberrant Behavior Checklist (irritability, hyperactivity) and on social awareness on the Social Responsiveness Scale, while the authors stop short of a general recommendation pending larger studies. [17]
Non-alcoholic fatty liver disease (NAFLD), hangover prevention, and general cleanse claims
InsufficientEvidenceinsufficientUK guidance leads, and there is none to support these uses: there is no GB-authorised health claim for NAC, no NHS or NICE pathway listing it for liver protection, hangover prevention or "cleansing", and the GB Nutrition and Health Claims Register holds no entry for it. Beneath that, the research is correspondingly thin — no robust systematic-review evidence supports these popular online uses, and liver-protection marketing in particular conflates the (well-established) intravenous antidote role in paracetamol overdose with a (very different) chronic oral-supplement use. [16]
Safety
NAC is generally well tolerated as a short-term oral supplement, but it has real interactions to be aware of (notably with nitrates and anticoagulants), can rarely trigger asthma-like bronchospasm, and is not a substitute for medical care in any of its better-known clinical contexts (paracetamol overdose, COPD). Talk to a pharmacist before starting if any of the scenarios below apply.
Talk to your pharmacist or GP first if you:
- You take a nitrate medicine for angina (glyceryl trinitrate / GTN spray, isosorbide mononitrate / dinitrate) — combining with NAC can cause a significant additional drop in blood pressure.
- You take an anticoagulant (warfarin, apixaban, rivaroxaban, dabigatran, edoxaban) or an antiplatelet (clopidogrel) — theoretical interaction; check before starting.
- You have asthma — IV and inhaled NAC have rarely caused paradoxical bronchospasm; oral capsules have been associated with respiratory symptoms in case reports.
- You take activated charcoal (e.g. for poisoning) — charcoal binds NAC and reduces absorption; separate doses if both are needed.
- You take gold-containing antirheumatic medicines (auranofin) — historic interaction caution.
- You are pregnant, breastfeeding, or thinking of becoming pregnant — supplemental NAC outside the IV antidote setting has limited safety data; talk to your GP or midwife.
- You have ever had a paracetamol overdose, or have taken more paracetamol than the maximum daily dose in the last 24 hours — go to A&E or call NHS 111. Oral NAC capsules are not a home antidote.
- You are taking NAC for depression, OCD, or any other psychiatric symptom — UK NHS care pathways apply; do not stop prescribed medication.
Pregnancy and breastfeeding
IV N-acetylcysteine is used in pregnant women in the antidote setting for paracetamol overdose, and that use is well established. Routine food-supplement NAC use in pregnancy has no UK guideline endorsement and limited safety data. Talk to your GP or midwife before supplementing during pregnancy.
Limited data. Talk to your pharmacist or GP.
Talk to your GP, midwife, or pharmacist before starting any supplement during pregnancy or breastfeeding.
More clinical detail (for clinicians and informed readers)
Contraindications
- Known hypersensitivity to N-acetylcysteine.
- Active asthma exacerbation — defer until stable; discuss with a clinician.
Drug interactions
- Nitrates (glyceryl trinitrate / GTN, isosorbide mononitrate, isosorbide dinitrate) — co-administration potentiates vasodilation and can produce a clinically significant additional fall in blood pressure with headache; reported in human pharmacology studies.
- Anticoagulants (warfarin, apixaban, rivaroxaban, dabigatran, edoxaban) and antiplatelets (clopidogrel, aspirin at antiplatelet dose) — theoretical additive bleeding risk; clinical-significance evidence limited but worth flagging to a prescriber.
- Activated charcoal — adsorbs NAC and reduces oral absorption; if both are clinically required, separate dosing.
- Gold-containing antirheumatic medicines (auranofin) — historic chelation interaction; specialist advice required.
- Carbamazepine — case-report suggestion of altered carbamazepine levels; monitor.
- ACE inhibitors and other antihypertensives — theoretical additive blood-pressure-lowering effect; clinical significance modest but worth noting if you are starting NAC alongside a new antihypertensive.
This is not an exhaustive list. Always tell your prescriber and pharmacist about every supplement you take.
Common side effects
- Nausea, vomiting, abdominal discomfort, diarrhoea — usually mild, dose-related.
- Sulphurous (egg-like) taste or smell — characteristic of cysteine derivatives.
- Headache.
Rare side effects
- Hypersensitivity reactions — rash, urticaria, angioedema.
- Paradoxical bronchospasm in people with asthma or other reactive airways disease (mostly described with IV / inhaled NAC, with case reports for oral).
- Anaphylactoid reactions — well-documented with IV NAC at high concentrations during paracetamol overdose treatment, rare with oral capsule use.
How to take it
- Typical supplemental range
- UK food-supplement products are most commonly sold at 600 mg per capsule, with directions for one to two capsules daily (600-1,200 mg/day). Pharmacist-supplied oral mucolytic preparations on the Continent (e.g. Fluimucil) are dosed at 600 mg two to three times daily. Mental-health RCTs (Berk 2008 bipolar depression) used 1,000 mg twice daily; some psychiatric trials have gone up to 2,400-3,600 mg/day in divided doses. There is no UK-authorised dose for food-supplement use, because there is no UK-authorised health claim.
- Timing
- No specific UK guidance for food-supplement use. The mucolytic pharmacist-supply tradition is to take with food to reduce GI upset.
How to spot quality
Look for
- Form named explicitly as N-acetyl-L-cysteine (or N-acetylcysteine) with the per-capsule milligram dose stated.
- GMP-certified UK or EU manufacture.
- Capsule shell named (HPMC for vegan / vegetarian; gelatin otherwise).
- Clean excipient list — anti-caking agents named, no proprietary blends hiding active dose.
- Third-party Certificate of Analysis available on request, with a recent date and a named batch.
- Honest marketing — no antidote framing, no liver-cleansing or body-cleansing framing, no mental-health treatment language, no hangover claims.
Red flags
- Liver-cleanse or liver-rescue framing on the label or PDP — NAC's antidote use is in IV hospital medicine, not in capsules.
- Hangover-prevention or post-drinking-recovery framing — no UK-authorised claim, no robust evidence.
- Long-COVID treatment claims — unsubstantiated.
- Antidepressant or anti-anxiety framing — NAC is not a UK-licensed mental-health medicine.
- Combined with high-dose niacin / methylation / cleanse stacks pitched as a system — that is marketing architecture, not formulation rationale.
- No batch / CoA traceability, or a CoA dated more than two years before purchase.
Commonly combined with
Other ingredients that share a biological pathway, cofactor relationship, or evidence-backed protocol with this one. Mechanisms below cite primary physiology — not folk pairing. Doses are literature ranges, not recommendations. Talk to your pharmacist or GP before changing your stack, especially if you take prescription medication.
Milk Thistle (Silybum marianum)
Limited evidenceLiver-cluster pairing — NAC glutathione precursor + silymarin antioxidant + membrane stabilisation.
NAC delivers cysteine substrate for glutathione synthesis; silymarin scavenges hepatocyte ROS + stabilises membranes. Mechanism complementary on hepatic oxidative-stress axis. Camden milk-thistle covers cluster.
Evidence: Camden milk-thistle + NAC NB-435 cluster.
Doses studied: 600-1200 mg NAC + 200-600 mg silymarin daily.
Found in Camden: Purifera™ NAC N-Acetyl-Cysteine 600mg 120 Capsules
Alpha Lipoic Acid (ALA / thioctic acid)
Limited evidenceAntioxidant cluster — NAC + ALA both feed glutathione redox cycle.
NAC cysteine substrate; ALA glutathione recycling. Complementary on glutathione axis.
Evidence: Each has individual trial body.
Doses studied: 600-1200 mg NAC + 300-600 mg ALA daily.
Found in Camden: Purifera™ NAC N-Acetyl-Cysteine 600mg 120 Capsules
Vitamin C
Limited evidenceGlutathione-cycle pairing — NAC substrate + vitamin C reduction-cycling support.
NAC delivers cysteine for glutathione synthesis; vitamin C reduces oxidised glutathione back to active form. Mechanism complementary.
Evidence: UK Article 13.1 vitamin C oxidative-stress claim. [6]
Doses studied: 600-1200 mg NAC + 80-1000 mg vitamin C daily.
Found in Camden: Purifera™ NAC N-Acetyl-Cysteine 600mg 120 Capsules